System, method, and computer program product for servo compensator switching in high vibration environments

ABSTRACT

A tape drive system according to one embodiment includes a magnetic head having at least one servo sensor; a tape motion controller; a fine actuator; a skew actuator; a coarse actuator; and a control. The control is configured to perform various operations that help account for vibrations that effect track-following a servo track when operating a tape drive. Additional systems, methods and computer program products are also described.

BACKGROUND

The present invention relates to track-following a servo track in alongitudinal tape system, and more particularly, to track-following aservo track in high vibration environments.

Current longitudinal tape drives, such as IBM® LTO Generation 5 tapedrives, IBM® 3592E07 tape drives and later among others, have methods totrack-follow a servo track. The track-following is performed bymonitoring a position error signal (PES) which is produced by comparinga desired position to an actual position of the magnetic head over thetape.

As new tape drives and tape media are developed, track density of thetape media increases to provide more capacity using the same tape width.In order to accomplish this, track widths have become narrower. Whenthese tape media are used, the track following servo of the tape drivehas to perform better to properly follow the narrower track width. Toachieve this, in conventional systems, the track following servocompensator is enhanced, allowing better performance with narrower trackwidths. However, the enhanced servo compensator has problems operatingin vibration environments because the external vibrations tend to pushthe head off track while operating the tape drive.

BRIEF SUMMARY

A tape drive system according to one embodiment includes a magnetic headhaving at least one servo sensor for sensing a lateral position of themagnetic head with respect to at least one defined servo track of alongitudinal tape; a tape motion controller configured to operate atleast one drive motor to move the longitudinal tape longitudinally pastthe magnetic head; a fine actuator configured to translate the magnetichead laterally with respect to the longitudinal tape; a skew actuatorconfigured to translate the magnetic head rotationally with respect tothe longitudinal tape; a coarse actuator configured to translate thefine actuator laterally with respect to the longitudinal tape; and acontrol configured to: sense a first servo sensor of the at least oneservo sensor; determine position error between the magnetic head and adesired position related to the at least one defined servo track;provide signals to operate the fine actuator to translate the magnetichead laterally in a manner to reduce the determined position error;determine skew error between an angle of the magnetic head relative totape motion and a desired angle relative to the at least one definedservo track; provide signals to operate the skew actuator to translatethe magnetic head rotationally in a manner to reduce the determined skewerror; determine when the position error is greater than a positionerror threshold; determine when the skew error is greater than a skewerror threshold; transition from a write state to a monitor state whenthe determined position error is greater than a threshold error value;and transition the fine actuator from a normal compensation mode to ahigh energy compensation mode when the position error is greater thanthe position error threshold for a first predetermined period and theskew error is greater than the skew error threshold for a secondpredetermined period.

A method according to one embodiment includes sensing a servo sensorwhile a longitudinal tape is moved past a magnetic head, wherein theservo sensor is configured for sensing a lateral position of themagnetic head with respect to at least one defined servo track of thelongitudinal tape; determining position error between the magnetic headand a desired position related to the at least one defined servo track;providing signals to operate a fine actuator to translate the magnetichead laterally in a manner to reduce the determined position error,wherein the fine actuator is configured to translate the magnetic headlaterally with respect to the longitudinal tape; determining skew errorbetween an angle of the magnetic head relative to tape motion and adesired angle relative to the at least one defined servo track;providing signals to operate a skew actuator to translate the magnetichead rotationally in a manner to reduce the determined skew error,wherein the skew actuator is configured to translate the magnetic headrotationally with respect to the longitudinal tape; determining when theposition error is greater than a position error threshold; determiningwhen the skew error is greater than a skew error threshold; andtransitioning the fine actuator from a normal compensation mode to ahigh energy compensation mode when the position error is greater thanthe position error threshold for a first predetermined period and theskew error is greater than the skew error threshold for a secondpredetermined period.

A computer program product according to one embodiment includes acomputer readable storage medium having computer readable program codeembodied therewith. The computer readable program code includes computerreadable program code configured to sense a servo sensor while alongitudinal tape is moved past a magnetic head, wherein the servosensor is configured for sensing a lateral position of the magnetic headwith respect to at least one defined servo track of the longitudinaltape; computer readable program code configured to determine positionerror between the magnetic head and a desired position related to the atleast one defined servo track; computer readable program code configuredto provide signals to operate a fine actuator to translate the magnetichead laterally in a manner to reduce the determined position error,wherein the fine actuator is configured to translate the magnetic headlaterally with respect to the longitudinal tape, wherein the fineactuator is set to a normal compensation mode when a tape cartridgecomprising the longitudinal tape is loaded; computer readable programcode configured to determine skew error between an angle of the magnetichead relative to tape motion and a desired angle relative to the atleast one defined servo track; computer readable program code configuredto provide signals to operate a skew actuator to translate the magnetichead rotationally in a manner to reduce the determined skew error,wherein the skew actuator is configured to translate the magnetic headrotationally with respect to the longitudinal tape; computer readableprogram code configured to determine if the position error is greaterthan a position error threshold; computer readable program codeconfigured to determine if the skew error is greater than a skew errorthreshold; and computer readable program code configured to transitionthe fine actuator from the normal compensation mode to a high energycompensation mode when the position error is greater than the positionerror threshold for a first predetermined period and the skew error isgreater than the skew error threshold for a second predetermined period,wherein the fine actuator remains in the high gain compensation modeuntil the tape cartridge comprising the longitudinal tape is unloaded,and wherein the high energy compensation mode comprises using a highergain value than the normal compensation mode.

Other aspects and embodiments of the present invention will becomeapparent from the following detailed description, which, when taken inconjunction with the drawings, illustrates by way of example theprinciples of the invention.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a partially cut away view of an exemplary magnetic tape datastorage drive which may implement embodiments of the present invention.

FIG. 2 is a view of the data storage drive of FIG. 1 with the coverremoved, according to one embodiment.

FIG. 3 is a schematic view of the longitudinal tape, tape head and servosystem of FIG. 1, according to one embodiment.

FIG. 4 is a view of a magnetic tape head and compound actuator of thedata storage drive of FIG. 1, according to one embodiment.

FIG. 5 is a partially cutaway side view of the magnetic tape head andcompound actuator of FIG. 4, according to one embodiment.

FIG. 6 is a block diagram of an embodiment of the servo system of FIG.3.

FIG. 7 is a diagram showing various write states, according to oneembodiment.

FIG. 8 is a flow diagram of a method, according to one embodiment.

FIG. 9 is a schematic of a magnetic head assembly having a skewactuator, according to one embodiment.

DETAILED DESCRIPTION

The following description is made for the purpose of illustrating thegeneral principles of the present invention and is not meant to limitthe inventive concepts claimed herein. Further, particular featuresdescribed herein can be used in combination with other describedfeatures in each of the various possible combinations and permutations.

Unless otherwise specifically defined herein, all terms are to be giventheir broadest possible interpretation including meanings implied fromthe specification as well as meanings understood by those skilled in theart and/or as defined in dictionaries, treatises, etc.

It must also be noted that, as used in the specification and theappended claims, the singular forms “a,” “an” and “the” include pluralreferents unless otherwise specified.

The following description describes methods and systems for accountingfor vibrations that effect track-following a servo track when operatinga tape drive.

In one general embodiment, a tape drive system includes a magnetic headhaving at least one servo sensor for sensing a lateral position of themagnetic head with respect to at least one defined servo track of alongitudinal tape; a tape motion controller configured to operate atleast one drive motor to move the longitudinal tape longitudinally pastthe magnetic head; a fine actuator configured to translate the magnetichead laterally with respect to the longitudinal tape; a skew actuatorconfigured to translate the magnetic head rotationally with respect tothe longitudinal tape; a coarse actuator configured to translate thefine actuator laterally with respect to the longitudinal tape; and acontrol configured to: sense a first servo sensor of the at least oneservo sensor; determine position error between the magnetic head and adesired position related to the at least one defined servo track;provide signals to operate the fine actuator to translate the magnetichead laterally in a manner to reduce the determined position error;determine skew error between an angle of the magnetic head relative totape motion and a desired angle relative to the at least one definedservo track; provide signals to operate the skew actuator to translatethe magnetic head rotationally in a manner to reduce the determined skewerror; determine when the position error is greater than a positionerror threshold; determine when the skew error is greater than a skewerror threshold; transition from a write state to a monitor state whenthe determined position error is greater than a threshold error value;and transition the fine actuator from a normal compensation mode to ahigh energy compensation mode when the position error is greater thanthe position error threshold for a first predetermined period and theskew error is greater than the skew error threshold for a secondpredetermined period.

In another general embodiment, a method includes sensing a servo sensorwhile a longitudinal tape is moved past a magnetic head, wherein theservo sensor is configured for sensing a lateral position of themagnetic head with respect to at least one defined servo track of thelongitudinal tape; determining position error between the magnetic headand a desired position related to the at least one defined servo track;providing signals to operate a fine actuator to translate the magnetichead laterally in a manner to reduce the determined position error,wherein the fine actuator is configured to translate the magnetic headlaterally with respect to the longitudinal tape; determining skew errorbetween an angle of the magnetic head relative to tape motion and adesired angle relative to the at least one defined servo track;providing signals to operate a skew actuator to translate the magnetichead rotationally in a manner to reduce the determined skew error,wherein the skew actuator is configured to translate the magnetic headrotationally with respect to the longitudinal tape; determining when theposition error is greater than a position error threshold; determiningwhen the skew error is greater than a skew error threshold; andtransitioning the fine actuator from a normal compensation mode to ahigh energy compensation mode when the position error is greater thanthe position error threshold for a first predetermined period and theskew error is greater than the skew error threshold for a secondpredetermined period.

In one general embodiment, a computer program product includes acomputer readable storage medium having computer readable program codeembodied therewith. The computer readable program code includes computerreadable program code configured to sense a servo sensor while alongitudinal tape is moved past a magnetic head, wherein the servosensor is configured for sensing a lateral position of the magnetic headwith respect to at least one defined servo track of the longitudinaltape; computer readable program code configured to determine positionerror between the magnetic head and a desired position related to the atleast one defined servo track; computer readable program code configuredto provide signals to operate a fine actuator to translate the magnetichead laterally in a manner to reduce the determined position error,wherein the fine actuator is configured to translate the magnetic headlaterally with respect to the longitudinal tape, wherein the fineactuator is set to a normal compensation mode when a tape cartridgecomprising the longitudinal tape is loaded; computer readable programcode configured to determine skew error between an angle of the magnetichead relative to tape motion and a desired angle relative to the atleast one defined servo track; computer readable program code configuredto provide signals to operate a skew actuator to translate the magnetichead rotationally in a manner to reduce the determined skew error,wherein the skew actuator is configured to translate the magnetic headrotationally with respect to the longitudinal tape; computer readableprogram code configured to determine if the position error is greaterthan a position error threshold; computer readable program codeconfigured to determine if the skew error is greater than a skew errorthreshold; and computer readable program code configured to transitionthe fine actuator from the normal compensation mode to a high energycompensation mode when the position error is greater than the positionerror threshold for a first predetermined period and the skew error isgreater than the skew error threshold for a second predetermined period,wherein the fine actuator remains in the high gain compensation modeuntil the tape cartridge comprising the longitudinal tape is unloaded,and wherein the high energy compensation mode comprises using a highergain value than the normal compensation mode.

As will be appreciated by one skilled in the art, aspects of the presentinvention may be embodied as a system, method or computer programproduct. Accordingly, aspects of the present invention may take the formof an entirely hardware embodiment, an entirely software embodiment(including firmware, resident software, micro-code, etc.) or anembodiment combining software and hardware aspects that may allgenerally be referred to herein as “logic,” a “circuit,” a “module,” ora “system.” Furthermore, aspects of the present invention may take theform of a computer program product embodied in one or more computerreadable medium(s) having computer readable program code embodiedthereon.

Any combination of one or more computer readable medium(s) may beutilized. The computer readable medium may be a computer readable signalmedium or a computer readable storage medium. A computer readablestorage medium may be, for example, but not limited to, an electronic,magnetic, optical, electromagnetic, infrared, or semiconductor system,apparatus, or device, or any suitable combination of the foregoing. Morespecific examples (a non-exhaustive list) of the computer readablestorage medium would include the following: an electrical connectionhaving one or more wires, a portable computer diskette, a hard disk, arandom access memory (RAM), a read-only memory (ROM), an erasableprogrammable read-only memory (EPROM or Flash memory), an optical fiber,a portable compact disc read-only memory (CD-ROM), an optical storagedevice, a magnetic storage device, or any suitable combination of theforegoing. In the context of this document, a computer readable storagemedium may be any tangible medium that can contain, or store a programfor use by or in connection with an instruction execution system,apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent invention may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present invention are described below with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems) and computer program products according to embodiments of theinvention. It will be understood that each block of the flowchartillustrations and/or block diagrams, and combinations of blocks in theflowchart illustrations and/or block diagrams, can be implemented bycomputer program instructions. These computer program instructions maybe provided to a processor of a general purpose computer, specialpurpose computer, or other programmable data processing apparatus toproduce a machine, such that the instructions, which execute via theprocessor of the computer or other programmable data processingapparatus, create means for implementing the functions/acts specified inthe flowchart and/or block diagram block or blocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other devices to causea series of operational steps to be performed on the computer, otherprogrammable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

FIGS. 1 and 2 illustrate a magnetic tape data storage drive 10 whichwrites data 18 to and reads data from longitudinal tape comprisingmagnetic tape data storage media 11, according to one embodiment.

As is understood by those of skill in the art, magnetic tape datastorage drives, also called magnetic tape drives or tape drives, maytake any of various forms. The illustrated magnetic tape drive 10 movesthe magnetic tape 11 along a tape path in the longitudinal direction ofthe tape from a supply reel 12 in a magnetic tape data storage cartridge13 to a take-up reel 14. An example of a magnetic tape drive is the IBM®LTO (Linear Tape Open) magnetic tape drive. Another example of amagnetic tape drive is the IBM® TotalStorage Enterprise magnetic tapedrive. Both the above examples of magnetic tape drives employ singlereel tape cartridges 13. An alternative magnetic tape drive and magnetictape cartridge is a dual reel cartridge and drive in which both reels 12and 14 are contained in the cartridge.

The magnetic tape media 11 is moved in the longitudinal direction acrossa tape head 65. The tape head may be supported and laterally moved by acompound actuator 17 of a track following servo system. The magnetictape media is supported by roller tape guides 50, 51, 52, 53, which maybe flanged or flangeless, while the magnetic tape media is movedlongitudinally.

A typical magnetic tape data storage drive operates in both forward andreverse (backward) directions to read and write data. Thus, the magnetictape head 65 may comprise one set of read and write elements foroperating in the forward direction and another set for operating in thereverse direction, or alternatively, may have two sets of the readelements on either side of the write elements to allow the same writeelements to write in both directions while the two sets of read elementsallow a read-after-write in both directions, according to variousembodiments.

The magnetic tape data storage drive 10 comprises one or more controls20 for operating the magnetic tape data storage drive in accordance withcommands received from an external system. The external system maycomprise a network, a host system, a data storage library or automationsystem, a data storage subsystem, etc., as would be apparent to one ofskill in the art upon reading the present descriptions. A control 20typically comprises logic and/or one or more microprocessors with amemory 19 for storing information and program information for operatingthe microprocessor(s) and drive. The program information may be suppliedto the memory via the interface 21, by an input to the control 20 suchas a floppy disk, optical disk, Flash memory, CD-ROM, etc., or byreading from a magnetic tape cartridge, or by any other suitable deviceor methodology. The magnetic tape data storage drive 10 may comprise astandalone unit or comprise a part of a tape library or other subsystem,which may comprise the external system. The control, 20 also providesthe data flow and formatter for data to be read from and written to themagnetic tape media, as is known to those of skill in the art.

A cartridge receiver 39 is configured to receive a magnetic tapecartridge 13 oriented in a single direction, and to align the magnetictape cartridge, for example, with guide pin 41, with respect to thecartridge receiver. The proper orientation may be illustrated on thecartridge itself, for example, by arrow 42 on the cartridge. The properorientation may be enforced by the specific shape of the cartridge or byusing various notches that interact with the receiver, as is known tothose of skill in the art. The orientation of the magnetic tapecartridge is such that the magnetic tape 11 exits the cartridge at aspecified point of the cartridge receiver. A tape threading mechanismmay move the free end of the magnetic tape 11 from the magnetic tapecartridge 13 to a take up reel 14, for example, positioning the free endleader block at the central axis 75 of the take up reel. The magnetictape is thus positioned along the tape path.

In the illustrated embodiment, flanged or flangeless tape guide rollers50, 51, 52 and 53 each has a cylindrical surface 80, 81, 82, 83 orientedto provide a tape path for the magnetic tape 11 across the magnetic tapehead 65.

The tape path comprises at least one flanged or flangeless tape guideroller 50 positioned between the magnetic tape cartridge 13 and magnetictape head 65, and may comprise at least one flanged or flangeless tapeguide roller 50, 51 at either side of the magnetic tape head 65.Additional tape guide rollers or other types of guides may be provideddepending on the length and/or complexity of the tape path, andpreferably comprise flangeless tape guide rollers, such as tape guiderollers 52 and 53.

Referring to FIG. 3, the longitudinal tape 11 is moved across the tapehead 65 between reels 12 and 14 (the tape guide rollers are not shown)by reel motors 15 and 16 under the control of a tape motion controller75 of control 20 of FIG. 1. The reel motors are operated at variousspeeds as controlled by the tape motion controller to insure that themagnetic tape media leaves one reel at the same speed that it is woundonto the other reel. Referring again to FIG. 3, the tape motioncontroller also controls the torque applied to each drive motor 15 and16 to control the tension applied to the magnetic tape media at the tapehead 65.

The magnetic tape head 65 comprises a servo read head, reader, or sensor76 that senses a servo pattern recorded in a servo track 68 of the tape11. The servo read head may comprise a plurality of servo read sensorsat various positions of the magnetic head 65, and the servo track 68 maycomprise a number of parallel servo tracks at various positions acrossthe tape 11. As is understood by those of skill in the art, the servotracks typically extend in the longitudinal direction the full length ofthe tape, and are prerecorded and defined as a part of the manufacturingprocess of the tape cartridge 13. A data head 78, which may compriseseveral data read/write transducers, is shown positioned over a datatrack region 18 of the tape, for example, containing a plurality ofparallel data tracks. As is understood by those of skill in the art,typically, the defined servo tracks of magnetic tape systems areparallel to and offset from the data tracks. The servo track 68 isillustrated as a single line, for example a centerline of a servo trackthat is wide enough to allow a single servo track or set of tracks toallow serving of various sets of data tracks by offsetting the servohead from the centerline.

As the tape 11 is moved longitudinally along the tape path, the servoread head 76 reads the servo signals which are provided on a servosignal line 84 to a servo decoder 86. The servo decoder processes thereceived servo signals and generates a position signal that is providedon a position signal line 88 to a servo control 90. The servo control 90responds to seek signals to cause the compound actuator 17 to movebetween servo tracks, and responds to the position signals to cause theactuator 17 to follow the desired servo track.

As the longitudinal tape 11 is moved longitudinally across the magnetictape head 65, the tape tends to either stay on one side of the tape heador to shift from one side of the tape head to the other. If the tapeshifts, the shifting of the tape 11 results in shifting the servo track68 in the lateral direction, illustrated in FIG. 3 as shifting betweenlateral shift extreme 77 and lateral shift extreme 79, comprisinglateral shift excursions between the extremes.

Referring now to FIGS. 3, 4, and 5, the compound actuator 17 isillustrated according to one embodiment. The actuator 17 comprises anactuator arm 32 mounting the magnetic tape head 65. A coarse actuatormotor 59 drives a lead screw 36 to move fine actuator stage 44 at anaperture 44A in a vertical direction perpendicular to a base 55. Anaperture 44B is provided to receive an anti-rotation pin 34, and a loadspring 48 is provided between a housing 26 and the stage 44. A torsionspring 46 is fixed to the stage 44 and is coupled at its ends 46A and46B to the actuator arm 32 so that the stage 44 moves the head 65mounted on the actuator arm 32 in a vertical direction across the tape.

A fine actuator coil assembly 60 is attached to an end of the actuatorarm 32. The coil assembly 60 comprises a coil frame 71, a coil 72, and amandrel 74, in one embodiment. The coil 62 has an upper portion 72A anda lower portion 72B, and is disposed between magnets 40A and 40B held ina magnet housing 38 which are arranged to split the north and southpoles at approximately the line 70. The coil moves vertically uponapplication of a current at the coil 72 and causes the actuator arm 32to pivot about torsion spring 46 and move the tape head 65 transverselyof the tape 11 to make small adjustments such as in track followingmode.

The servo control 90 responds to the position signals to generate servocontrol signals on line 91 to operate the fine actuator 60 to follow thedesired servo track, and when the fine actuator movement is insufficientto accommodate the full move, or a large move is required for otherpurposes, the servo control 90 generates servo control signals on line93 to cause the coarse actuator 59 to move the fine actuator is thedesired direction.

Alternative compound actuators may be used as would be apparent to oneof skill in the art upon reading the present descriptions. Each compoundactuator has both a fine actuator providing high bandwidth, but with alimited range of travel, and a coarse actuator providing a large workingdynamic range.

A servo control 90 is illustrated in FIG. 6 as part of a position errorsignal (PES) loop 170 of a servo system 180, according to oneembodiment. The operation of the servo system is discussed in detail inU.S. Pat. No. 6,587,303. Briefly, the servo signals are sensed by servosensor 76 of head 65, and the position of the servo sensor relative to aservo track is detected from the servo signals by the signal decoder 86.The detected position signals are provided on line 88 and preferablycomprise digital signals. The position signals are then compared to areference signal 177 by a comparator 178 to determine position errorbetween the read and a desired position related to the defined servotracks, called the PES on line 179.

The fine actuator servo typically has a compensator function 185 in theposition error signal loop, which is designed to enable maximumbandwidth with adequate stability margins. The compensator function 185modifies the PES by applying a variable gain to the PES, which gain isbased upon the frequency of the input PES 179, or, from anotherviewpoint, upon the rates of change of the input PES.

The compensator function 185 includes an integrator 187 and othertransfer function elements, such as a lead/lag functional element 186,to achieve the desired static and dynamic system performance and overallstability. Each element may be implemented as a filter, either an analogfilter employing discrete components, or a digital filter, such as anIIR (infinite impulse response) or as a FIR (finite impulse response),or as microcode causing a microprocessor to perform the function.

The integrator 187 provides a response 200 that generally reduces thegain as the frequency increases. The lead/lag element 186 provides aresponse 201 which is enhanced at high frequencies and reduced at lowfrequencies. The combined response 205 provides a servo signal to thefine actuator 60 that has both high bandwidth and stability, as isunderstood by those of skill in the art. A digital to analog converter206 and power amplifier 207 apply the signal to the fine actuator 60.

The integrator 187 integrates the present signal, approximating thecurrent and therefore the force applied to the fine actuator, with priorsignals to determine the DC component of the fine actuator PES. Analternative integration function comprises determining the DC componentof the drive current for the fine actuator. The integration functionoutput signal on connection 200 provides an integration control signalto a driver 211, which drives the coarse actuator 59, operating thecoarse actuator to translate the fine actuator. If the coarse actuatoris a stepper motor, the driver 211 is preferably digital up-down logicand a stepper driver. Thus, if the absolute maximum value of theintegration function output signal is larger than the absolute minimumvalue, the driver 211 operates the stepper motor to step in a directionto center the maximum and minimum values of the integration outputsignal. A step of the stepper motor may result in a linear translationof the fine actuator, for example, of about 3 microns. Alternatively, inone approach, if the coarse actuator is analog, the driver 211 mayconvert the digital signal to analog and employ a power amplifier tooperate the coarse actuator 59.

The coarse actuator may also be operated by a seek function 183 whichmoves the fine actuator from one servo track to another.

The output 200 of the integrator is also supplied to a shift control 220in accordance with one embodiment which moves the coarse actuator to aspecific location and maintains it at that location.

According to one embodiment, by increasing the track-following gain inthe lower frequencies, the effects of any external vibrations may bepartially mitigated. However, this higher, low frequency gain cannot beused in normal, non-vibration environments because the servo willovershoot the desired track position, which leads to problems in servotrack-following control. Therefore, different servo compensation must beswitched in and out of operation when the drive operates in or out of avibration environment, according to one embodiment.

In one embodiment, a tape drive comprises two track-followingcompensation settings, one for non-vibration environments, and one forvibration environments. The track-following compensation may be switchedfrom one to the other on the fly without stopping reading and/orwriting. This allows the tape drive to have the more appropriatetrack-following compensation setting active according to the externalvibration environment of the tape drive.

In order to signal that a switch would be beneficial to the tape drive,two signals are monitored for evidence of a vibration environment. Usingthe two signals, in one approach, the vibration or non-vibrationenvironment may be detected and the track-following servo compensationmay be switched to a setting better suited for that environment (e.g.,vibration mode or normal mode). To avoid situations where transitoryvibration environments cause the tape drive to repeatedly switch fromnormal mode to vibration mode, and then back to normal mode over andover again, once the compensator is switched to the vibration mode, itstays in that mode until the tape cartridge is unloaded from the tapedrive. Each time a tape cartridge is inserted into the tape drive, thecompensator is reset back to the normal mode, e.g., the compensator isset to non-vibration environment settings.

The two signals that are monitored and used to indicate when a switch isappropriate are the Skew Error Signal (SES) and the Position ErrorSignal (PES). The SES is related to an amount that the magnetic head isangled relative to the longitudinal tape path as would be understood byone of skill in the art upon reading the present descriptions. In oneexample, the SES may be used in order to keep leading and trailingtransducers aligned to a single track of the tape.

In one embodiment, when the SES exceeds a SES threshold for more than apredetermined period, such as about 10, 20, 30, 40, or more consecutiveor near consecutive samples (for example, if 39 of 40 samples exceed thethreshold, or if 58 of 60 samples exceed the threshold, etc.), it isindicated that the SES threshold has been exceeded, such as by setting aSESflag to true (e.g., flipping an indicator bit from 0 to 1). And whenthe PES exceeds a PES threshold (for example, 16, 32, 64, 80, or morecounts) for more than a second predetermined period (for example, 10,20, 30, 40, or more consecutive or near consecutive samples), it isindicated that the PES threshold has been exceeded, such as by setting aPESflag to true (e.g., flipping an indicator bit from 0 to 1). The twoflags are monitored and when they are both true (e.g., each indicatorbit is 1), the compensation setting is switched from normal mode tovibration mode, e.g., the values best suited for a vibration environmentare used in the compensator, which is sometimes referred to as a “highenergy compensator.”

In one example, a test is shown below, where both flags are true and thecompensator is switched from normal to vibration mode.

SES>(SES Threshold, 100) for (1st Predetermined Period, 30 consecutivesamples)→SESflag=TRUE;

PES>(PES Threshold, 64) for (2nd Predetermined Period, 30 consecutivesamples)→PESflag=TRUE;

when ((PESflag=TRUE) AND (SESflag=TRUE))→COMPSETTING=HIGHENERGY.

According to one embodiment, as shown in FIG. 7, interactions andtransitions between writing states may be described. When the tapedrive, a control such as a servo control, or some other logic,component, and/or system is in the Write State 702, which may bereferred to in code as TFSAL_Enable, write operations are enabled andthe servo track is track-followed using any method as would beunderstood by one of skill in the art upon reading the presentdescriptions.

If an error occurs other than a position-related error, such as an errorindicated by the position error (such as PES) or skew error (such asSES), the tape drive, a control such as a servo control, or some otherlogic, component, and/or system is transitioned to the Stop Write State704. Errors other than position-related errors include a PES_STATUSerror, LongErasure error, and/or other errors as would be understood byone of skill in the art upon reading the present descriptions.

During track-following, position error is monitored and if the positionerror (such as PES, as described herein) exceeds a PES threshold, whichmay be predefined by a user, administrator, in logic, or stored incomputer readable program code, the tape drive, a control such as aservo control, or some other logic, component, and/or system may betransitioned into a Monitor State 706. The PES threshold, as previouslydescribed, may be a predefined number of counts, such as 16, 32, 64,etc., that when this many position errors are detected, it may beassumed that the servo track-following is having difficulty inpositioning the magnetic head over the servo track.

When the tape drive, a control such as a servo control, or some otherlogic, component, and/or system is in the Monitor State 706, which maybe referred to in code as Monitor_PESBehavior, write operations aredisabled and the servo track is continued to be track-followed using anymethod as would be understood by one of skill in the art upon readingthe present descriptions.

Once again, during the track-following, PES is monitored and if theposition error exceeds the threshold position error for a predeterminedperiod, which may be defined by a user or administrator, and may berelated to any factor as would be understood by one of skill in the art,the tape drive, a control such as a servo control, or some other logic,component, and/or system may be transitioned into a Stop Write State704.

When the tape drive, a control such as a servo control, or some otherlogic, component, and/or system is in the Stop Write State 704, whichmay be referred to in code as PrepareForStopWrite, write operations aredisabled and the servo track is no longer track-followed.

The tape drive, a control such as a servo control, or some other logic,component, and/or system remains in the Stop Write State 704 until thetape drive, a control such as a servo control, or some other logic,component, and/or system progresses through an intermediate write state(not pictured) which may comprise one or more steps or processes beforethe tape drive, a control such as a servo control, or some other logic,component, and/or system is allowed to enter the Write State 702 again.

Also, the tape drive, a control such as a servo control, or some otherlogic, component, and/or system may transition into a Servo State 710from the Write State 702 or the Monitor State 706 when a band checkerror is indicated, such that the DAC OUT is at a maximum value for apredetermined period. In the Servo State 710, write operations aredisabled and servo track-following is in a parked position which is usedwhen the servo track is not being track-followed.

Prom the Monitor State 706, the tape drive, a control such as a servocontrol, or some other logic, component, and/or system may transitioninto a Slew Stop Write State 708 where write operations are disabled andthe compound actuator is slowly moved in order to better track-followthe servo track, since the Monitor State 706 has been active for solong, it is an indication that track-following is not performingeffectively.

During any of the states (Write State 702 and/or Monitor State 706) theSES is monitored in addition to the PES, as previously described foreach state. If both switching conditions are met, e.g., SES>(SESThreshold) for (1st Predetermined Period) AND PES>(PES Threshold) for(2nd Predetermined Period), then the compensator is set to the vibrationmode, e.g., the compensator settings are changed to the high gaincompensator settings to account for observed vibration in the followingstates: Stop Write State 704, Slew Stop Write State 708, and/or ServoState 710.

Now referring to FIG. 8, a method 800 is shown according to oneembodiment. The method 800 may be carried out in any desiredenvironment, including those shown in FIGS. 1-7, and 9, according tovarious embodiments. Of course, more or less operations than thosespecifically described below may be included and/or excluded from method800, according to various embodiments, as would be apparent to one ofskill in the art upon reading the present descriptions.

In preliminary operations, a tape may be loaded in a tape drive and atape motion controller may operate at least one drive motor to move thetape longitudinally past a magnetic head. Also, the servo signal may beacquired from a servo sensor, such as by a signal decoder, in someapproaches.

In operation 802, the servo sensor is sensed while a longitudinal tapeis moved past a magnetic head, wherein the servo sensor is configuredfor sensing a lateral position of the magnetic head with respect to atleast one defined servo track of the longitudinal tape.

In operation 804, position error is determined between the magnetic headand a desired position related to the at least one defined servo track.This position error may be related to the DC component of the fineactuator PES, in some embodiments.

According to some embodiments,

In operation 806, signals are provided to operate a fine actuator totranslate the magnetic head laterally in a manner to reduce thedetermined position error. The fine actuator is configured to translatethe magnetic head laterally with respect to the longitudinal tape.

In one embodiment, while the servo signal is track-followed, anintegrator may effectively integrate signals representing the forceapplied to the fine actuator and may indicate the present position ofthe servo track with respect to the coarse actuator, for example,ultimately reaching “0.” Shift control determines, from the integrator,the DC component of the position error signal. This “0” position is oneextreme of the lateral shift of the tape.

In operation 808, skew error is determined between an angle of themagnetic head relative to tape motion and a desired angle relative tothe at least one defined servo track.

In operation 810, signals are provided to operate a skew actuator totranslate the magnetic head rotationally in a manner to reduce thedetermined skew error. The skew actuator is configured to translate themagnetic head rotationally with respect to the longitudinal tape,according to one embodiment.

In operation 812, it is determined when the position error is greaterthan a position error threshold. This may be determined based on thePES.

In operation 814, it is determined when the skew error is greater than askew error threshold.

In operation 816, the fine actuator is transitioned from a normalcompensation mode to a high energy compensation mode when the positionerror is greater than the position error threshold for a firstpredetermined period and the skew error is greater than the skew errorthreshold for a second predetermined period.

Any of several factors, as would be understood by one of skill in theart upon reading the present descriptions, may be used to dictate thefirst and/or second predetermined period for how long the PES and/or SESis greater than the PES/SES threshold. For example, some factors mayrelate to what caused the position error and/or skew error in the firstplace. For example, this period may be 10, 15, 30, 40, or more servosamples or interrupt cycles (typically about 50 μsec each), in variousembodiments.

In another embodiment, the first and/or predetermined periods maycomprise at least one of: a number of position error samples beingdetermined, a number of skew error samples being determined, an amountof time, and an amount of tape movement in the longitudinal direction,as would be understood by one of skill in the art upon reading thepresent descriptions.

Referring now to FIG. 9, a magnetic head assembly 900 having a skewactuator 908 is shown, according to one embodiment. The skew actuator908 is connected to a fine actuator 902 by a connecting bar 910, or someother suitable device for translating movement, and provides rotationalmobility 916 to the magnetic head 904 and fine actuator 902 along apivot point 906, according to one embodiment.

The pivot point 906 may be located at any position of the magnetic headassembly 900, and is shown centered as one embodiment. The rotation ofthe magnetic head 904 about the pivot point 906 causes rotationalmovement 916.

In some embodiments, where the skew error between an angle of themagnetic head relative to tape motion and a desired angle relative tothe servo track is determined to be greater than a skew error threshold,the skew actuator 908 may translate along a longitudinal direction 912in order to rotate the magnetic head 904 in an attempt to correct thedetermined skew error. This translational movement is transferred fromthe skew actuator 908 to the magnetic head 904 and fine actuator 902 viathe connecting bar 910 and converted into rotational motion 916 alongthe pivot point 906.

In operation, the skew actuator 908 and magnetic head assembly 900 arecapable of precisely and flexibly adjusting a position of the magnetichead 904 along a lateral direction 914 via lateral motion by the fineactuator 902, as well as along a rotational direction 916 vialongitudinal motion 912 by the skew actuator 908 and connecting bar 910.

Of course, other rotational actuators may be used to adjust for observedskew error as would be understood by one of skill in the art uponreading the present descriptions, and the method of adjusting for skewerror is not limited to this single embodiment.

In one embodiment, the high energy compensation mode may comprise usinga higher gain value than the normal compensation mode. In furtherembodiments, it may use different lead/lag functional elements toaccomplish better control in a vibration environment, as would beunderstood by one of skill in the art upon reading the presentdescriptions.

Also, during PES and SES monitoring, the number of servo samples ismonitored and if a predetermined number of samples (such as 5 samples,10 samples, 20 samples, 30 samples, etc.) have passed without thePES/SES value returning into an acceptable range (e.g., below thePES/SES threshold), the tape drive, a control such as a servo control,or some other logic, component, and/or system may transition to the stopwrite state where the track-following servo is interrupted (the servoloop is opened). Once in this state, the track-following servo moves toa different set of states and procedures where it once again tries tore-acquire the servo signal when appropriate. Also, the fine actuatormay be transitioned into the high energy compensation mode in oneapproach.

According to some embodiments, the tape drive may be used inenvironments having high vibration where the number of stop write eventsoccur very frequently. Using conventional methods, the lost tapecapacity would be excessive and would cause the tape capacity to dropbelow market (and/or advertised) value. However, by implementing thehigh energy compensation mode to the fine actuator in the tape drive,the servo track-following is much better, and so when vibrations causetrack-following issues, their effect is minimal on tape capacity losses.

In one embodiment, the longitudinal tape may comprise a plurality of thedefined servo tracks and a plurality of data bands, each data bandpositioned between two of the defined servo tracks. In a furtherembodiment, the threshold error value may relate to about 25%, 50%, 80%,120%, or some other fraction or multiple of a distance between the atleast one defined servo track and an adjacent servo track of theplurality of servo tracks.

In another embodiment, the PES threshold may be in a range from about0.5 μm to about 1.5 μm of lateral tape movement, such as about 0.8 μm oflateral tape movement.

In yet another embodiment, the SES threshold may be in a range fromabout 5 μm to about 15 μm of relative head position, such as about 10 μmof relative head position.

In some approaches, the fine actuator remains in the high energycompensation mode until a tape cartridge comprising the longitudinaltape is unloaded, and the fine actuator is set to the normalcompensation mode when a tape cartridge comprising the longitudinal tapeis loaded, thereby allowing the method 800 to be repeated for each newtape cartridge.

Any of the implementations and/or embodiments described herein mayinvolve software, firmware, micro-code, hardware and/or any combinationthereof. The implementation may take the form of code or logicimplemented in a medium in the control (20, FIG. 1), such as memory,storage and/or circuitry where the medium may comprise hardware logic(e.g., an integrated circuit chip, Programmable Gate Array (PGA),Application Specific Integrated Circuit (ASIC), or other circuit, logicor device), or a computer readable storage medium, such as a magneticstorage medium, e.g., an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, semiconductor or solid state memory,magnetic tape, a removable computer diskette, and random access memory(RAM), a read-only memory (ROM), a rigid magnetic disk and an opticaldisk, compact disk-read only memory (CD-ROM), compact disk-read/write(CD-R/W), digital versatile disk (DVD), etc.

For example, in one embodiment, a tape drive system, such as tape drive10 shown in FIG. 1, may comprise a magnetic head, such as tape head 65,comprising at least one servo sensor, such as sensor 76, the servosensor being for sensing a lateral position of the magnetic head withrespect to at least one defined servo track, such as servo track 68, ofa longitudinal tape, such as tape 11, a tape motion controller, such astape motion controller 75, configured to operate at least one drivemotor, such as drive motors 15 and 16, to move the longitudinal tapelongitudinally past the magnetic head, a fine actuator, such as fineactuator 60, configured to translate the magnetic head laterally withrespect to the longitudinal tape, a skew actuator configured totranslate the magnetic head rotationally with respect to thelongitudinal tape, a coarse actuator, such as coarse actuator 59,configured to translate the fine actuator laterally with respect to thelongitudinal tape, and a control, such as control 20 and/or servocontrol 90. The control may be configured to sense a first servo sensorof the at least one servo sensor, determine position error between themagnetic head and a desired position related to the at least one definedservo track, provide signals to operate the fine actuator to translatethe magnetic head laterally in a manner to reduce the determinedposition error, determine skew error between an angle of the magnetichead relative to tape motion and a desired angle relative to the atleast one defined servo track, provide signals to operate the skewactuator to translate the magnetic head rotationally in a manner toreduce the determined skew error, determine when the position error isgreater than a position error threshold, determine when the skew erroris greater than a skew error threshold, transition from a write state toa monitor state when the determined position error is greater than athreshold error value, and transition the fine actuator from a normalcompensation mode to a high energy compensation mode when the positionerror is greater than the position error threshold for a firstpredetermined period and the skew error is greater than the skew errorthreshold for a second predetermined period.

In more approaches, the high energy compensation mode may comprise usinga higher gain value than the normal compensation mode, among otherchanges to the compensation function as would be understood by one ofskill in the art.

In some embodiments, the first and/or second predetermined periods mayeach comprise at least one of: a number of position error samples beingdetermined (such as 10, 20, 30, 40, or more), a number of skew errorsamples being determined (such as 10, 20, 30, 40, or more), an amount oftime (such as 1 μsec, 2 μsec, 5 μsec, 10 μsec, or more), and an amountof tape movement in the longitudinal direction (such as 10 μm, 100 μm,500 μm, 1000 μm, or more).

In more embodiments, the longitudinal tape may comprise a plurality ofthe defined servo tracks and a plurality of data bands, each data bandpositioned between two of the defined servo tracks. In theseembodiments, the position error threshold may be related to about 25%,50%, 75%, etc., of a distance between the at least one defined servotrack and an adjacent servo track of the plurality of servo tracks.

According to another embodiment, the position error threshold may be ina range from about 0.5 μm to about 1.5 μm of lateral tape movement, suchas about 0.8 μm of lateral tape movement.

In another embodiment, the skew error threshold may be in a range fromabout 5 μm to about 15 μm of relative head position, such as about 10 μmof relative head position.

In one approach, the control may be configured to maintain the fineactuator in the high gain compensation mode until a tape cartridgecomprising the longitudinal tape is unloaded. This prevents jumping fromthe normal to the high energy compensation mode, which may interrupttape drive functions or introduce more errors. Also, in preferredembodiments, when a tape cartridge comprising the longitudinal tape isloaded into the tape drive, the control may be configured to set thefine actuator in the normal compensation mode.

In more embodiments, methods and/or techniques described hereinaccording to various embodiments may be embodied in a computer programproduct. For example, in one embodiment, a computer program product maycomprise a computer readable storage medium having computer readableprogram code embodied therewith. The computer readable program code maycomprise computer readable program code configured to: sense a servosensor while a longitudinal tape is moved past a magnetic head, whereinthe servo sensor is configured for sensing a lateral position of themagnetic head with respect to at least one defined servo track of thelongitudinal tape; determine position error between the magnetic headand a desired position related to the at least one defined servo track;provide signals to operate a fine actuator to translate the magnetichead laterally in a manner to reduce the determined position error,wherein the fine actuator is configured to translate the magnetic headlaterally with respect to the longitudinal tape, wherein the fineactuator is set to a normal compensation mode when a tape cartridgecomprising the longitudinal tape is loaded; determine skew error betweenan angle of the magnetic head relative to tape motion and a desiredangle relative to the at least one defined servo track; provide signalsto operate a skew actuator to translate the magnetic head rotationallyin a manner to reduce the determined skew error, wherein the skewactuator is configured to translate the magnetic head rotationally withrespect to the longitudinal tape; determine when the position error isgreater than a position error threshold; determine when the skew erroris greater than a skew error threshold; and transition the fine actuatorfrom the normal compensation mode to a high energy compensation modewhen the position error is greater than the position error threshold fora first predetermined period and the skew error is greater than the skewerror threshold for a second predetermined period. The fine actuatorremains in the high gain compensation mode until the tape cartridgecomprising the longitudinal tape is unloaded, and the high energycompensation mode comprises using a higher gain value than the normalcompensation mode.

Of course, any of the embodiments described previously may beimplemented in the computer program product. For example, in oneembodiment, the computer readable program code may be configured totransition from the stop write state to a write preparation state whenthe determined position error is greater than a multiple of thethreshold error value or greater than the threshold error value for athird predetermined period. While in the write preparation state, writeoperations are disabled, a first servo sensor is sensed, position erroris determined between the magnetic head and a desired position relatedto the at least one defined servo track, and signals are provided tooperate the fine actuator to translate the magnetic head laterally in amanner to reduce the determined position error in an attempt tore-acquire a lock on the at least one defined servo track.

While various embodiments have been described above, it should beunderstood that they have been presented by way of example only, and notlimitation. Thus, the breadth and scope of an embodiment of the presentinvention should not be limited by any of the above-described exemplaryembodiments, but should be defined only in accordance with the followingclaims and their equivalents.

What is claimed is:
 1. A tape drive system, comprising: a magnetic headhaving at least one servo sensor for sensing a lateral position of themagnetic head with respect to at least one defined servo track of alongitudinal tape; a tape motion controller configured to operate atleast one drive motor to move the longitudinal tape longitudinally pastthe magnetic head; a fine actuator configured to translate the magnetichead laterally with respect to the longitudinal tape; a skew actuatorconfigured to translate the magnetic head rotationally with respect tothe longitudinal tape; a coarse actuator configured to translate thefine actuator laterally with respect to the longitudinal tape; and acontrol configured to: sense a first servo sensor of the at least oneservo sensor; determine position error between the magnetic head and adesired position related to the at least one defined servo track;provide signals to operate the fine actuator to translate the magnetichead laterally in a manner to reduce the determined position error;determine skew error between an angle of the magnetic head relative totape motion and a desired angle relative to the at least one definedservo track; provide signals to operate the skew actuator to translatethe magnetic head rotationally in a manner to reduce the determined skewerror; determine when the position error is greater than a positionerror threshold; determine when the skew error is greater than a skewerror threshold; transition from a write state to a monitor state whenthe determined position error is greater than a threshold error value;and transition the fine actuator from a normal compensation mode to ahigh energy compensation mode when the position error is greater thanthe position error threshold for a first predetermined period and theskew error is greater than the skew error threshold for a secondpredetermined period.
 2. The tape drive system as recited in claim 1,wherein the high energy compensation mode comprises using a higher gainvalue than the normal compensation mode.
 3. The tape drive system asrecited in claim 1, wherein the first predetermined period comprises atleast one of: a number of position error samples being determined, anumber of skew error samples being determined, an amount of time, and anamount of tape movement in the longitudinal direction.
 4. The tape drivesystem as recited in claim 1, wherein the second predetermined periodcomprises at least one of: a number of position error samples beingdetermined, a number of skew error samples being determined, an amountof time, and an amount of tape movement in the longitudinal direction.5. The tape drive system as recited in claim 1, wherein the longitudinaltape comprises a plurality of the defined servo tracks and a pluralityof data bands, each data band positioned between two of the definedservo tracks.
 6. The tape drive system as recited in claim 5, whereinthe position error threshold is related to about 50% of a distancebetween the at least one defined servo track and an adjacent servo trackof the plurality of servo tracks.
 7. The tape drive system as recited inclaim 1, wherein the position error threshold is in a range from about0.5 μm to about 1.5 μm of lateral tape movement.
 8. The tape drivesystem as recited in claim 1, wherein the position error threshold isabout 0.8 μm of lateral tape movement.
 9. The tape drive system asrecited in claim 1, wherein the skew error threshold is in a range fromabout 5 μm to about 15 μm of relative head position.
 10. The tape drivesystem as recited in claim 1, wherein the skew error threshold is about10 μm of relative head position.
 11. The tape drive system as recited inclaim 1, wherein the control is configured to maintain the fine actuatorin the high gain compensation mode until a tape cartridge comprising thelongitudinal tape is unloaded.
 12. The tape drive system as recited inclaim 1, wherein the control is configured to set the fine actuator inthe normal compensation mode when a tape cartridge comprising thelongitudinal tape is loaded.
 13. A method, comprising: sensing a servosensor while a longitudinal tape is moved past a magnetic head, whereinthe servo sensor is configured for sensing a lateral position of themagnetic head with respect to at least one defined servo track of thelongitudinal tape; determining position error between the magnetic headand a desired position related to the at least one defined servo track;providing signals to operate a fine actuator to translate the magnetichead laterally in a manner to reduce the determined position error,wherein the fine actuator is configured to translate the magnetic headlaterally with respect to the longitudinal tape; determining skew errorbetween an angle of the magnetic head relative to tape motion and adesired angle relative to the at least one defined servo track;providing signals to operate a skew actuator to translate the magnetichead rotationally in a manner to reduce the determined skew error,wherein the skew actuator is configured to translate the magnetic headrotationally with respect to the longitudinal tape; determining when theposition error is greater than a position error threshold; determiningwhen the skew error is greater than a skew error threshold; andtransitioning the fine actuator from a normal compensation mode to ahigh energy compensation mode when the position error is greater thanthe position error threshold for a first predetermined period and theskew error is greater than the skew error threshold for a secondpredetermined period.
 14. The method as recited in claim 13, wherein thehigh energy compensation mode comprises using a higher gain value thanthe normal compensation mode.
 15. The method as recited in claim 13,wherein the first and second predetermined periods comprise at least oneof: a number of position error samples being determined, a number ofskew error samples being determined, an amount of time, and an amount oftape movement in the longitudinal direction.
 16. The method as recitedin claim 13, wherein the longitudinal tape comprises a plurality of thedefined servo tracks and a plurality of data bands, each data bandpositioned between two of the defined servo tracks.
 17. The method asrecited in claim 13, wherein the position error threshold is in a rangefrom about 0.5 μm to about 1.5 μm of lateral tape movement.
 18. Themethod as recited in claim 13, wherein the skew error threshold is in arange from about 5 μm to about 15 μm of relative head position.
 19. Themethod as recited in claim 13, wherein the fine actuator remains in thehigh energy compensation mode until a tape cartridge comprising thelongitudinal tape is unloaded, and wherein the fine actuator is set tothe normal compensation mode when a tape cartridge comprising thelongitudinal tape is loaded.
 20. A computer program product comprising anon-transitory computer readable storage medium having computer readableprogram code embodied therewith, the computer readable program codecomprising: computer readable program code configured to sense a servosensor while a longitudinal tape is moved past a magnetic head, whereinthe servo sensor is configured for sensing a lateral position of themagnetic head with respect to at least one defined servo track of thelongitudinal tape; computer readable program code configured todetermine position error between the magnetic head and a desiredposition related to the at least one defined servo track; computerreadable program code configured to provide signals to operate a fineactuator to translate the magnetic head laterally in a manner to reducethe determined position error, wherein the fine actuator is configuredto translate the magnetic head laterally with respect to thelongitudinal tape, wherein the fine actuator is set to a normalcompensation mode when a tape cartridge comprising the longitudinal tapeis loaded; computer readable program code configured to determine skewerror between an angle of the magnetic head relative to tape motion anda desired angle relative to the at least one defined servo track;computer readable program code configured to provide signals to operatea skew actuator to translate the magnetic head rotationally in a mannerto reduce the determined skew error, wherein the skew actuator isconfigured to translate the magnetic head rotationally with respect tothe longitudinal tape; computer readable program code configured todetermine if the position error is greater than a position errorthreshold; computer readable program code configured to determine if theskew error is greater than a skew error threshold; and computer readableprogram code configured to transition the fine actuator from the normalcompensation mode to a high energy compensation mode when the positionerror is greater than the position error threshold for a firstpredetermined period and the skew error is greater than the skew errorthreshold for a second predetermined period, wherein the fine actuatorremains in the high gain compensation mode until the tape cartridgecomprising the longitudinal tape is unloaded, and wherein the highenergy compensation mode comprises using a higher gain value than thenormal compensation mode.